This invention relates to new unsaturated polyester resins based on selected starting materials, to a process for their preparation and to compositions containing these polyester resins as essential component.
Unsaturated polyester resins have long been known as binders for coatings cured by UV radiation. Thus according to DE-AS 1 694 149, mixtures of unsaturated polyesters and polymerisable monomers may be cured by UV radiation with the addition of certain benzoin compounds. Due to the inhibiting action of atmospheric oxygen, lacquers based on these systems are frequently not sufficiently hardened on the surface and therefore cannot be sanded down but good rubbing down of the layer of primer is essential for obtaining lacquer film surfaces of good appearance on wood.
The method of preventing the inhibitory action of air on the conventional hardening of lacquers with peroxide by adding paraffin ("paraffin polyesters") which become deposited on the surface in the process of gelling is only applicable with reservations because the thermal energy emitted from the UV radiators prevents the formation of a protective film of paraffin. In such cases, it is necessary first to pass the material through a so called pregelling zone.
Unsaturated polyesters containing .alpha.,.beta.-unsaturated dicarboxylic acid groups and allyl ether and/or polyalkylene glycol groups ("gloss polyesters") do not require paraffin for curing the surface of the lacquer film since the ether groups release an auto-oxidative drying process. UV-curing of such resins containing allyl ether groups (DE-OS 2 113 998) or polyalkylene glycol groups (DE-OS 3 010 428) results in lacquer films which are easily rubbed down in much the same way as conventional curing but the reactivity of such resins is often too low to ensure sufficient processing speeds.
It was therefore an object of the present invention to provide new polyester resins which do not have the disadvantages mentioned above, i.e. which are in particular suitable for the preparation of coating compounds which can be cured by UV radiation and combine good levelling with rapid curing and give rise to lacquer films with surfaces which can easily be rubbed down.
It was surprisingly found that this problem could be solved by providing the polyester resin according to the invention described in detail below or mixtures containing these polyester resins as essential component.